Network Working Group B. Wellington
Request for Comments: 3007 Nominum
Updates: 2535, 2136 November 2000
Obsoletes: 2137
Category: Standards Track
Secure Domain Name System (DNS) Dynamic Update
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This document proposes a method for performing secure Domain Name
System (DNS) dynamic updates. The method described here is intended
to be flexible and useful while requiring as few changes to the
protocol as possible. The authentication of the dynamic update
message is separate from later DNSSEC validation of the data. Secure
communication based on authenticated requests and transactions is
used to provide authorization.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
1 - Introduction
This document defines a means to secure dynamic updates of the Domain
Name System (DNS), allowing only authorized sources to make changes
to a zone's contents. The existing unsecured dynamic update
operations form the basis for this work.
Familiarity with the DNS system [RFC1034, RFC1035] and dynamic update
[RFC2136] is helpful and is assumed by this document. In addition,
knowledge of DNS security extensions [RFC2535], SIG(0) transaction
security [RFC2535, RFC2931], and TSIG transaction security [RFC2845]
is recommended.
Wellington Standards Track [Page 1]RFC 3007 Secure Dynamic Update November 2000
This document updates portions of RFC 2535, in particular section
3.1.2, and RFC 2136. This document obsoletes RFC 2137, an alternate
proposal for secure dynamic update, due to implementation experience.
1.1 - Overview of DNS Dynamic Update
DNS dynamic update defines a new DNS opcode and a new interpretation
of the DNS message if that opcode is used. An update can specify
insertions or deletions of data, along with prerequisites necessary
for the updates to occur. All tests and changes for a DNS update
request are restricted to a single zone, and are performed at the
primary server for the zone. The primary server for a dynamic zone
must increment the zone SOA serial number when an update occurs or
before the next retrieval of the SOA.
1.2 - Overview of DNS Transaction Security
Exchanges of DNS messages which include TSIG [RFC2845] or SIG(0)
[RFC2535, RFC2931] records allow two DNS entities to authenticate DNS
requests and responses sent between them. A TSIG MAC (message
authentication code) is derived from a shared secret, and a SIG(0) is
generated from a private key whose public counterpart is stored in
DNS. In both cases, a record containing the message signature/MAC is
included as the final resource record in a DNS message. Keyed
hashes, used in TSIG, are inexpensive to calculate and verify.
Public key encryption, as used in SIG(0), is more scalable as the
public keys are stored in DNS.
1.3 - Comparison of data authentication and message authentication
Message based authentication, using TSIG or SIG(0), provides
protection for the entire message with a single signing and single
verification which, in the case of TSIG, is a relatively inexpensive
MAC creation and check. For update requests, this signature can
establish, based on policy or key negotiation, the authority to make
the request.
DNSSEC SIG records can be used to protect the integrity of individual
RRs or RRsets in a DNS message with the authority of the zone owner.
However, this cannot sufficiently protect the dynamic update request.
Using SIG records to secure RRsets in an update request is
incompatible with the design of update, as described below, and would
in any case require multiple expensive public key signatures and
verifications.
Wellington Standards Track [Page 2]RFC 3007 Secure Dynamic Update November 2000
SIG records do not cover the message header, which includes record
counts. Therefore, it is possible to maliciously insert or remove
RRsets in an update request without causing a verification failure.
If SIG records were used to protect the prerequisite section, it
would be impossible to determine whether the SIGs themselves were a